The Isuzu I-Mark brake light requires a 1157 bulb size for proper illumination and function. Data for the specific bulb requirements covers the period from 1981 through 1989.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Isuzu I-Mark uses the 1157 bulb for brake lighting across the 1981-1989 model years.
The 1157 is a dual-filament bulb operating at 12V with a 21W/5W output rating, meaning its two filaments serve separate functions at different wattages within the same housing.
The 1157 uses a BAY15d bayonet base, a two-pin offset base design that physically prevents incorrect single-filament bulbs from being seated in its socket.
The 1156 bulb is specified for the Center High Mount Stop Light on the Isuzu I-Mark for the 1987-1989 model years.
The 1156 operates at 12V with a single 21W filament, making it a single-function bulb suited only for on/off lighting applications such as a dedicated stop light.
The 1156 uses a BA15s bayonet base, a single-pin design that is not interchangeable with the BAY15d base of the 1157, despite the two bulbs sharing the same 15mm base collar width.
Both the 1157 and 1156 are ANSI-standardized bulbs recognized across the United States and Canada, meaning their electrical and physical specifications conform to a common North American standard.
The physical and electrical differences between the 1157 and 1156, particularly their base pin configurations and filament counts, mean one cannot serve as a direct replacement for the other.